1. Technical Field
The present invention relates to a semiconductor circuit, a battery monitoring system, and a diagnosis method. The present invention particularly relates to a semiconductor circuit that measures the voltage of plural serially connected batteries and to a battery monitoring system, and a diagnosis method of the same.
2. Related Art
High capacity, high output batteries employed for example for motor drive in hybrid vehicles and electric vehicles generally employ a battery configured from plural serially connected batteries (battery cells) (a specific example being a lithium ion battery). Known battery monitoring systems for monitoring and control measure the battery voltage of the cells of such a battery.
A related battery monitoring system is known that measures the battery voltage of each battery cell by the difference between the voltage at the high voltage side and the voltage at the low voltage side of plural serially connected battery cells. For example, technology is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2010-16928 wherein any (two) terminals to which power supply lines connected to respective battery cells are connected are selected by a multiplexer, and output to a differential amplifier. Analog electrical signals output from the differential amplifier are converted to digital electrical signals and then output. The battery voltage of the respective battery cells is measured based on the digital electrical signals.
A digital measurement instrument including a self-diagnostic function is also disclosed in JP-A No. 8-189845. In the digital measurement instrument disclosed in JP-A No. 8-189845, as illustrated in FIG. 10, a single input circuit is configured by a range switching circuit 109 that switches the gain, and includes a function for performing self-diagnosis of the single input circuit (the range switching circuit 109). In the range switching circuit 109 illustrated in FIG. 10, the gain is switched by connecting switching elements SW192, 193 connected to an NC side or to an NO side.
For example, if the gain of the range switching circuit 109 is denoted gain G1 and gain G2, then the ratio between the gain G1 and the gain G2 is derived by inputting a reference voltage A to the range switching circuit 109, and performing analogue to digital (AD) conversion of value G1×A obtained as gain G1, and value G2×A obtained as gain G2. Diagnosis is then made as to whether or not the gain switching is correct.
However, in the technology disclosed in JP-A No. 8-189845, since in the range switching circuit 109 the precision of the gain G1 itself and the gain G2 itself is diagnosed, the precision of the reference voltage A must be the same as or better than the input-output conversion precision of the circuit subject to self-diagnosis.
In the self-diagnosis technology of JP-A No. 8-189845, when applied to a differential input circuit as the circuit for self-diagnosis, a reference voltage B (power source for supplying the reference voltage B) is required to additionally supply the reference voltage B to perform self-diagnosis due to there being to two systems for input. An issue thus arises in that, similarly to with the reference voltage A described above, the precision of the reference voltage B must also be the same as or greater than the input-output conversion precision of the circuit subject to self-diagnosis.
Hence in a battery monitoring system such as that of the technology disclosed in JP-A No. 2010-16928, a differential amplifier is employed, and the above issue arises when the self-diagnosis technology of the JP-A No. 8-189845 is applied to self-diagnosis technology of a differential amplifier. As a result there is a concern of being unable to perform self-diagnosis appropriately.